This invention relates to tape cassettes and, more particularly to a means for preventing rotation of the tape reels of a video cassette
For convenience of reference, when describing the tape cassette of the prior art and the present invention, "inward" means in a direction toward to the interior of the cassette from its sides, "outward" means in a direction toward the sides of the cassette from the interior, "upward" means in a direction toward the cassette cover from the cassette base, and "downward" means in a direction toward the base from the cover.
A conventional tape cassette has a flat, substantially rectangular configuration, which may be formed of a suitable plastic, and includes a cassette base and cover, each having side walls. Tape reels are usually suitably located in side-by-side relation within the cassette so as to be freely rotatable, and a magnetic tape is wound on the tape reels.
Each reel is intentionally made to float independently relative to its respective hub receptacle formed in the cassette base due to various industry tolerances. Further, as tape is wound from one reel to another, the tape mass on each reel changes. Under these conditions, one reel may shift or float backwardly, while the other is shifted toward the front. A reel lock must compensate for these shifts, so that both reels are reliably and independently locked.
The industry has almost uniformly adopted a multipiece, reel lock, such as shown and described in U.S. Pat. Nos. 4,447,020 or 4,232,840. Such multipiece reel locks include a separate actuator, a pair of separate movable arms for respectively locking the reels, and a separate spring for biasing the arms toward the reels. This design efficiently compensates for reel shifting because each arm can lock independently.
Of course, such a multipiece lock, despite its known reliability, is rather expensive to produce and assemble. Further, due to the number of parts and the fabrication requirements for each part, production yields cannot be maximized.
Due to these drawbacks, attempts have been made to make the actuator, reel lock and spring one piece to cut down on manufacturing and assembly costs. For example, as described in U.S. Pat. No. 4,739,949 and as shown in FIG. 1 herein, a reel lock can be molded as a single piece of flexible elastic plastic material.
More particularly, a front bottom edge 1a of a locking base 1 is shaped as an inclined surface to receive a conventional tape player/recorder pin (not shown) during operation. Each side of a back edge 1b of the locking base 1 includes a concave fixing wing 11. The bottom of the free end of each fixing wing 11 locks with serrations 31 positioned peripherally around the tape reels 3.
The locking base 1 is located within two, parallel guiding walls 21 that are formed at the middle inside of the cassette base 2. The guiding walls 21 are as high as the locking base 1. Opposing slots (not shown) are formed in the guiding walls 21 to enable the locking base 1 to move without obstructing movement of the fixing wings 11. In addition, at the two sides of the parallel guiding walls 21 are positioned two supporting walls 22 which respectively cantilever support the fixing wings 11 so as to solidly stop the tape reels while the locking base 1 is in the locking position.
As the cassette is put into a tape player/recorder, the pin rises into a hole 24 formed in the cassette base 2 and pushes the locking base 1 out of the locked position. Meanwhile, the fixing wings 11 of the locking base 1, because of the backward movement of the locking base 1 and the interference of the supporting walls 22, move backward and additionally inward so that they are released from the serrations 31 of the reels, which can then rotate freely.
When the tape cassette is ejected, the locking base 1, because it is no longer being pushed by the pin of the recorder, immediately returns by its inherent resilience back to its normal "locked" position and meshes in one of the serrations 31 of the reels 3 via the fixing wings 11.
As can be seen, this structure strongly locks the reels in position. The problem with this approach, as discussed above, is that each reel floats independently relative to the hub receptacles. As such, when one reel floats and positions itself toward the back of the cassette and the other reel moves forward, integral reel locks such as the device of the '949 patent are incapable of reliably locking both reels under these conditions, so tape unravelling is not indeed accomplished. The integral actuator/reel lock/spring described in U.S. Pat. No. 4,449,677 suffers from the same problem. Because of this significant drawback, integral actuator/reel lock/springs have not been adopted by the industry, even though they represent substantial cost savings.